Heterocysts with reduced cell walls in populations of cycad cyanobionts

The ultrastructure of the cyanobionts of the greenhouse-grown cycads Cycads circinalis, Ceratozamia mexicana, and Encephalartos villosus was studied. In addition to heterocysts with the typical ultrastructure, the cyanobiont microcolonies also contained altered heterocysts with reduced cell walls, which might dominate in all regions of the coralloid roots. The altered heterocysts represented a protoplast enclosed in a heterocyst-specific envelope with additional layers. Some heterocysts contained an additional reticular protoplast-enclosing sheath below the heterocyst-specific envelope, whereas the other heterocysts contained an additional electron-opaque outer layer. The substance of the inner sheath of the former heterocysts resembled the polysaccharides of mucilage, which fills the intercellular space of plant tissues, whereas the electron-opaque outer layer of the latter heterocysts probably had a protein nature. The substances that constitute the sheath and the outer layer are likely to be synthesized intracellularly and then released with the aid of membrane-bounded vesicles or by channels in the cytoplasmic membrane.     

Desmodesmus sp. 3Dp86E-1—a Novel Symbiotic Chlorophyte Capable of Growth on Pure CO2

A novel chlorophyte Desmodesmus sp. 3Dp86E-1 isolated from a White Sea hydroid Dynamena pumila was cultivated at CO₂ levels from atmospheric (the ‘low-CO₂’ conditions) to pure carbon dioxide (the 5, 20, and 100 % CO₂ conditions) under high (480 μE/(m² s) PAR) light. After 7 days of cultivation, the ‘100 % CO₂’ (but not 5 or 20 % CO₂) cells possessed ca. four times higher chlorophyll content per dry weight (DW) unit than the low-CO₂ culture. The rate of CO₂ fixation under 100 % CO₂ comprised ca. 1.5 L/day per L culture volume. After a lag period which depended on the CO₂ level, biomass accumulation and volumetric fatty acid (FA) content of the Desmodesmus sp. 3Dp86E-1 bubbled with CO₂-enriched gas mixtures increased and was comparable to that of the culture continuously bubbled with air. Under the low-to-moderate CO₂ conditions, the FA percentage of the algal cells increased (to 40 % DW) whereas under high-CO₂ conditions, FA percentage did not exceed 15 % DW. A strong increase in oleate (18:1) proportion of total FA at the expense of linolenate (18:3) was recorded in the ‘100 % CO₂’ cells. Electron microscopy and pulse–amplitude-modulated chlorophyll fluorescence investigation revealed no damage to or significant downregulation of the photosynthetic apparatus in ‘100 % CO₂’ cells grown at the high-PAR irradiance. Possible mechanisms of high-CO₂ tolerance of Desmodesmus sp. 3Dp86E-1 are discussed in view of its symbiotic origin and possible application for CO₂ biomitigation.     

Molecular phylogeny of a green microalga isolated from White Sea sponge <Emphasis Type="Italic">Halichondria panicea</Emphasis> (Pallas, 1766)

Molecular identification of eukaryotic microalga 1Hp86E-2 isolated from White Sea sponge Halichondria panicea (Pallas, 1766) was conducted, and phylogenetic analysis was carried out using the nucleotide sequence of 18S rRNA gene (GenBank, no. JX437624). Isolated microalga was classified to the genus Desmodesmus. Microalga 1Hp86E-2 proved to be closely related to the algae Desmodesmus sp. 3Dp86E-1, Desmodesmus sp. 2C166E, and Desmodesmus sp. 1Pm66B isolated from White Sea invertebrates. Phylogenetic analysis showed that these closely related organisms belong to a monophyletic group.     

Permeability of cyanobacterial mucous surface structures for macromolecules

The space of diffusive distribution of neutral hydrophilic macromolecules (dextrans with molecular sizes of 1.5 to 9 nm in the Stokes’ radius values) in the mucous surface structures (MSS) of intact bacterial cells has been studied for the first time on cyanobacteria. Cyanobacterial species and strains under study belong to different taxonomic groups, the members of which form MSS of various morphology and ultrastructure and can grow in association with plants and animals, inter alia as mucous microcolonies. The range of permeability has been determined by the fractionation of polydisperse dextrans method, previously applied for plants, in combination with electron microscopy. Dextrans are supposedly distributed in the MSS polysaccharide matrix in accordance with their sizes, in much the same way as in a macroporous unitary gel. The similarity of the chemical composition and macromolecular organization of cyanobacterial MSS with pectins of plant cell walls and the role of MSS and the intercellular matrix as permeability barriers in associative interactions of microorganisms are under consideration.     

Permeability of cyanobacterial mucous surface structures for macromolecules

The space of diffusive distribution of neutral hydrophilic macromolecules (dextrans with molecular sizes of 1.5 to 9 nm in the Stokes radius values) in the mucous surface structures (MSS) of intact bacterial cells has been studied for the first time on cyanobacteria. Cyanobacterial species and strains under study belong to different taxonomic groups, the members of which form MSS of various morphology and ultrastructure and can grow in association with plants and animals, inter alia as mucous microcolonies. The range of permeability has been determined by the fractionation of polydisperse dextrans method, previously applied for plants, in combination with electron microscopy. Dextrans are supposedly distributed in the MSS polysaccharide matrix in accordance with their sizes, in much the same way as in a macroporous unitary gel. The similarity of the chemical composition and macromolecular organization of cyanobacterial MSS with pectins of plant cell walls and the role of MSS and the intercellular matrix as permeability barriers in associative interactions of microorganisms are under consideration.     

Atypical cell forms overproducing extracellular substances in population of cycad cyanobionts

The ultrastructure of the cyanobionts of the greenhouse-grown cycads Cycas circinalis, Ceratozamia mexicana, and Encephalartos villosus was studied. The cyanobiont microcolonies grown in the intercellular space of the cyanobacterial zone of cortical parenchyma in the cycad coralloid roots contained two specific forms of vegetative cells with a reduced cell wall, namely, protoplasts and spheroplasts. The protoplasts and spheroplasts exhibited ultrastructural changes indicating the overproduction of two extracellular substances, one of which resembled the mucilage polysaccharides and the other was proteinous. The substances were likely to be synthesized intracellularly and then be excreted with the aid of surface vesicles or by channels in the cytoplasmic membrane to form, respectively, a slimy extracellular matrix and an additional electron-opaque envelope around the cell. At the late developmental stages, the excretion of these substances was accompanied by degradative changes in the cells, leading eventually to cell death. The physiological role of these specific cell forms and the factors that induce their development and death in the cell populations of cyanobionts are discussed.     

MiRNA miR-375 as a Multifunctional Regulator of the Cardiovascular System

Molecular Biology - MicroRNA (miRNA) miR-375 acts as a multifunctional regulator of the activity of many physiological and pathological cellular processes by interacting with a large number of...